Enhancement trench type power MOSFETs are well known. Such devices employ a conventional base or channel region which is inverted by gate potential applied to polysilicon gates buried in the trenches and insulated from the trench walls by a gate oxide or other oxide layers.
In the Depletion Trench MOSFET it is the accumulation region (as opposed to inversion region) that provides the device conduction as well as the bulk of the mesa.
The impurity concentration of the mesa regions and the body below the trenches in such devices is relatively low in order to provide a suitable blocking voltage when the device is off, and to allow use of a low threshold gate voltage for turning the device on. This low body concentration, however, increases the device on-resistance RDSON.